Is the conversion harness for the 13 pin plug? You could have just moved the 2 pins and removed the 3rd and been good. The bigger problem you are going to have is in your PCM. There is a place to select 4l80 but to the best of my knowledge, the calibration is not there. You would need a 4l80 segment from a PCM with the same OS loaded into your PCM. Look on HPtuner site for more info. I'm in the same boat right now with a 99 manual equipped Corvette com that a guy wants to run a 4l60 in.
You can add the pins and I have some that I can send you. It takes the same plug as the rear one. WPVSS30 is the pn. It's on Amazon for under $15.
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